Blades and blade assemblies for turbine engines,compressors and the like



R. E. BEER ET AL 3,515,499 BLADES AND BLADE ASSEMBLIES FOR TURBINE 2 Sheets-Sheet 1 June; 2, 1970 ENGINES, COMPRESSORS AND THE LIKE Filed April 22, 1968 is ii m m i R0004! E. BEER. CLARf/YC E E. KL$S/G, RICHARD -J. LA 49072,

INVENTOR5.

June 2, 1970 R. E. BEER ET AL 3,515,499

BLADES AND BLADE ASSEMBLIES FOR TURBINE ENGINES, COMPRESSORS AND THE LIKE Filed April 22, 1968 2 Sheets-Sheet 2 86 FIG. /3 L i R0000 E. 555 a4 .ez-wrs 4-. Me 54 INVENTOR5.

ArrbzmeK United States Patent US. Cl. 41695 20 Claims ABSTRACT OF THE DISCLOSURE Blades and blade assemblies for use in turbine engines, compressors and the like comprising a stack of a plurality of discrete wafers bonded together to form a unitary structure. A controlled pattern of flow passages is provided on a planar surface of each wafer and a means is provided for delivering coolant to the flow passages. Slots are provided in the edge surface of each wafer and each slot is in fluid communication with a fiow passage on each of the wafers. The slots and flow passages may be curved to improve cooling of the blade assembly. The wafers are sufficiently thin to permit thermal equilibrium between the wafers and the coolant in the flow passages so that maximum exploitation of the coolant is attained.

This invention relates to blades and blade assemblies for use in turbine engines, gas turbines, steam turbines, compressors and the like.

In-their most basic form, turbine engines include a combustion chamber, a compressor located at the inlet of the combustion chamber for delivering compressed gas to the combustion chamber, and a turbine driven by the hot combustion gases exhausted from the combustion chamber. In most conventional turbine engines, the turbine drives the compressor. Both the compressor and the turbine include a plurality of radially disposed blades. One set of blades, often referred to as the stator blades or vanes, is fixedly mounted to the turbine or compressor so as to direct gas toward the rotor blades. The rotor blades rotate about the axis along which the gas flows. In the case of a turbine, the stator blades direct the axially flowing combustion gases toward the rotor blades causing rotation of the rotor. The rotor of the turbine is usually connected by means of a shaft to the rotor of the compressor, thereby rotating the compressor rotor. The rotation of the compressor rotor directs gas flowing through the compressor toward the stator blades of the compressor, thereby compressing the gas drawn into the combustion chamber.

Heretofore, blades for turbines, compressors and the like have been subject to failure due to ineffective cooling of the blade surface. The ineffective cooling of prior blades was caused by several factors, such as the inability to control wall permeability during manufacture and the fact that the individual pores often closed, or became plugged, due to oxidation of the porous passages, deposit formation over the pores, and particulate matter in the coolant.

It is an object of the present invention to provide blades and blade assemblies for turbine engines, compressors and the like wherein the blades are effectively cooled to prevent damage to the blades.

Another object of the present invention is to provide ice blades and blade assemblies constructed from a stack of wafers, the wafers having passages for coolant flow to cool the surfaces of the blades and the blade wall.

Another object of the present invention is to provide blades which are cooled by convection cooling, film cooling, transpiration cooling or any combination thereof.

Another object of the present invention is to provide both stator and rotor blades for blade assemblies which are effectively cooled by coolant flow.

A blade according to the present invention comprises a stack of a plurality of wafers. A controlled pattern of flow passages is provided on a planar surface of each wafer and means is provided for delivering coolant to the flow passages.

According to an optional and desirable feature of the present invention, slots are provided in the surface of the blade, each slot being in fluid communication with one or more flow passages.

According to another optional and desirable feature of the present invention, the Wafers are radially disposed to form rotor blades or stator vanes.

The present invention offers significant advantages over conventional cooling techniques in the following respects:

(1) Precise flow control.Control of the flow of the coolant can be accurately maintained by varying the depth, width or length of the passages through the wafer, and providing internal manifold sizes conforming to the flow desired.

(2) Failure protection-The wafer type cooling design is not susceptible to failure caused by high pressure coolant erupting through a failure opening in the blade wall, since it is not necessary to maintain the coolant at a high pressure. Furthermore, localized overheating will not result in hot spot instability because the local coolant flow is uncoupled from the surface heat flux through the use of hydraulically isolated parallel coolant flow passages which have their hydraulic resistance significantly removed from the heated surface.

(3) Cooling effectiveness.By permitting excellent thermal communication between the metal of the wall and the coolant at all points within the wall, the cooling capability of the coolant is completely exploited and the cooling efficiency is maximized.

(4) Fabrication simplicity-Due to the basic simplicity and repetitious nature of the resign, the same technology can be applied to blades of all sizes. In addition, larger blades can be fabricated by using a number of smaller easily constructed modules.

The above and other features of this invention will be more fully understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a partly cutaway perspective view of a blade assembly utilizing a stack of a plurality of wafers according to the presently preferred embodiment of the present invention;

FIGS. 29 are top view elevations of various modifications of wafers for use in the blade assembly illustrated in FIG. 1.

FIG. 10 is a partly cutaway perspective view of another embodiment of a blade assembly utilizing a stack of a plurality of wafers according to the present invention;

FIGS. 11 and 12 are top view elevations of various modifications of wafers for use in the blade assembly illustrated in FIG. 10; and

FIG. 13 is a partly cutaway perspective view of another modification of a blade according to the present invention.

Referring to FIG. 1 there is illustrated a blade assembly accordingto the presently preferred embodiment of the present invention. The blade assembly includes a blade mounted to wall 12, such as a wall of a turbine engine. Although FIG. 1 illustrates only one blade, it is to be understood that an ordinary blade assembly includes a plurality of blades, the number of blades being determined by the designer to accommodate the particular design.

Blade 10 is constructed of a stack of a plurality of wafers or platelets 14 having a thickness between about 0.002 and 0.030 inch. The peripheral wall of each wafer 14 forms an enclosed chamber 16 adapted to be connected in fluid communication with a supply of coolant fluid. Structural partitions 18 may be incorporated within chamber 16 to provide several coolant passages in the event different pressures are to be maintained in the separate passages to control the pressure differential across various portions of the wall of each wafer 14. In addition, the structural partitions 18 also function as strengthening members for the walls of the wafers. Each wafer includes a plurality of pores 20 in fluid communication with chamber 16. Each pore 20 preferably has a hydraulic diameter of between approximately 0.002 and 0.010 inch and is in fluid communication with a slot 22. Slots 22 each have a width approximately equal to the diameter of an associated pore and is of such length as to be in fluid communication with a pore through each of several wafers. By way of example, as illustrated in FIG. 1, each slot 22 is formed through five wafers and is in fluid communication with a pore in each of the five wafers. Slots 22 provide fluid communication between the pores and an edge surface of the wafer. Each wafer illustrated in FIG. 1 further includes a distribution channel 24 to provide fluid communication between chamber 16 and pores The individual wafers may be formed in any one of several different ways. One method known to those skilled in the art is the photo-etching process. With the photoetching process, a thin metal sheet is imprinted with an acid-resistant ink which outlines all the flow passages. The sheet is then immersed in an acid bath which etches out the flow paths at a precisely known, predetermined rate. Several depths of etch can be obtained on a single sheet of stock by repeating the above process with different patterns. In this way it is possible to form slots 22 completely through the thin stock while forming pores 20 only partially therethrough.

It should be pointed out that it is possible to form the individual wafers by a variety of other methods, such as by embossing them or by electroplating areas to form raised areas rather than etching out the depressed areas. Other means include, but are not limited to, the utilizing of the crude etching process in the formation of all the passages with the exception of the pores which may be provided by a scribing process similar to that used in preparing defraction gradings. The slots, pores and channels can also be obtained by conventional identation processes or forming rolls. These methods are likewise well known to those skilled in the art.

The completed wafers 14 are then stacked together so that the planar surface of one wafer abuts the planar surface of the next wafer to form the blade 10. For some applications it may be desirable to bond the wafers together. Bonding of the wafers 14 can be accomplished in several different ways. One method is to electroplate to-the thin sheet stock a thin flash of braze material prior to applying acid-resistant ink. The wafers so constructed will be provided with a coating of brazing alloy on all surfaces which contact adjoining wafers, but with none in any passageway through which coolant will be permitted to flow. The entire blade 10 may then be placed in a furnace and brazed together.

Other methods which might be used for joining the wafers together are diffusion bonding, resistance welding, or simply applying some advanced bonding agent to th contacting surfaces.

When fully assembled, wafers 14- form the completed blade 10 which may be assembled to the walls 12, such as by brazing, welding, or other method. By way of example, wall 12 may be constructed of a plurality of wafers 28 having a plurality of flow passages 30 connected in fluid communication to a distribution passage 32. Passages 32 are connected in fluid communication to a suitable source of coolant. A suitable construction for wall 12 is more fully described in co-pending application Ser. No. 656,522, filed July 27, 1967, by Robert J. Kuntz et al., entitled Transpiration Cooled Devices, and assigned to the same assignee as the present invention.

Chamber 16 is connected to a fluid manifold (not shown) which supplies coolant to chamber 16 within blade 10. The coolant is permitted to flow through pores 20 and into slot 22. This arrangement permits coolant fluid to flow through slots 22 to the edge surface of the wafers to permit a film of coolant to form over the exterior wall surface of blade 10. The trailing edge of the blade illustrated in FIG. 1 is cooled by convection, due to coolant flowing through channels 24 and pores 26. Thus, the blade illustrated in FIG. 1 provides convection-film cooling of the head and body portions of the blade and convection cooling of the trailing edge.

In FIGS. 2 and 3 there is illustrated a Wafer 14a and 14b, a stack of which may be utilized to form blade 10 in FIG. 1, to provide film cooling of the entire surface of the blade, including the trailing edge. Wafer 14a utilizes a plurality of pores 20 and slots 22 arranged in a similar manner to wafer 14 in FIG. 1. The pores 20 and slots 22 of wafer 14a are arranged in such a manner as to provide film cooling of the entire surface of the blade due to coolant flowing through chamber 16 and manifold 34. Manifold 34 is connected in fluid communication with the source of coolant. Pores 36 are in fluid communication with manifold 34 to provide coolant flow to slots 38. Slots 38 provide film cooling of the trailing edge of the blade, and coolant flow through slots 38 may be separately regulated by means of suitable control means connected to manifold 34.

As illustrated in FIG. 1, structural support 18 may be integrally formed by each Wafer 14. Alternatively, the wafers 14 may be constructed as illustrated in FIGS. 2 and 3 having slots 40 within the walls of the wafers so that insert 18a may be inserted within slots 40 to provide the structural support.

FIG. 4 illustrates another embodiment of a wafer for use in a blade. Wafer 14c provides film cooling of the body and head of the blade and combined film convection cooling of the trailing edge. In this case, pores 20 are in fluid communication with chamber 16 and provide coolant flow to slots 22. Manifold 34 is in fluid communication with slots 38 through pores 36 and is in fluid communication with channel 42 to pore 26. Manifold 34 supplies coolant flow through pores 36 to slots 38 thereby providing film cooling of the trailing edge of the blade. In addition, manifold 34 provides coolant flow through channel 42 and pore 26 to provide convection cooling of the trailing edge of the blade.

As illustrated in FIG. 4, slots 22 may be designed so as to provide an oblique angle so that the body and head portions of the blade may be convection cooled as coolant passes through the slots. When coolant reaches the edge surfaces of the wafers, it forms a film over the blade thereby film-cooling the head and body of the blade.

FIG. 5 illustrates an arrangement for a wafer 14a for use in a blade similar to that shown in FIG. 4. However, in the case of FIG. 5, slots 22 are curved toward the trailing edge of the blade to reduce flow resistance of coolant through the slots. FIG. 5 further illustrates that the trailing edge of the blade may be convection cooled with several channels 42.

FIG. 6 illustrates a wafer 14e having a plurality of manifolds 44 in fluid communication with slots 46 through pores 48. Manifolds 44 are connected in fluid communication to a source of coolant so that coolant flows through manifolds 44, pores 46 and into slots 48. Since the manifolds are placed in close proximity to the edge surfaces of the wafers 14e, coolant flow through manifold 44 provides convection cooling of the surface of the blade. In addition, coolant flow through pores 46 and slots 48 provides film cooling of the surface of the blade so that the blade is cooled by combined convection and film cooling.

FIG. 7 illustrates another modification of a wafer 14f for use in a blade wherein slots 22 are of a tortuous design having the appearance of a lazy S shape to provide convection cooling of the surface of the blade formed by wafers 14] due to coolant flowing through the extended center portions of the slots. The slots are arranged so that coolant tends to flow toward the trailing edge of the blade.

FIG. 8 illustrates another modification of a wafer 14g having a plurality of pores providing fluid communication between coolant chamber 16 and the edge surface of the wafer. As illustrated in FIG. 8, the pores may be curved, angled or even straight. In addition, the trailing edge of the blade formed by wafers 14g may be cooled by means of channel 42 and additional pores 20a.

FIG. 9 illustrates another modification wherein wafer 1411 is provided with tortuous pores 22b and flared pores 22c. The tortuous pores provide convection cooling of the surface of a blade formed by wafers 14h, while flared pores 22c provide transpiration cooling of the surface. If desired, flow diverters 22d, in the form of small islands, may be placed in the flared portions of pores 22c.

FIGS. 1-9 illustrate several of the embodiments for wafers for use in cooling a blade. Of course, several of the designs illustrated in FIGS. l-9 may be combined to provide convection cooling of certain areas of the blade and film cooling of other areas of the blade, and combined convection and film cooling of yet other areas of the blade. Furthermore, the specific designs of the flow passages, slots and pores through the wafers for the coolant may be varied in accordance with a wide number of modifications.

Heretofore, the present disclosure has described blades utilizing a stack of a plurality of wafers each disposed in a plane substantially tangential to the axis of the turbine engine or gas compressor. It should be understood that the wafers may be disposed in any desired plane. For example, in FIG. 10 there is illustrated a blade assembly utilizing wafers which are disposed in a plane radial to the axis of the gas generator or turbine engine.

In FIG. 10 there is illustrated a blade mounted to a wall 62 such as a rotor of a turbine engine. Blade 60 is constructed of a stack of a plurality of wafers 64 each having a distribution channel 66 in fluid communication with a manifold 68. Flow passages 70 are in fluid communication with an edge surface of each Wafer thereby providing a substantially porous wall surface for the blade. Restrictor passages 72 meter coolant flow from distribution channels 66 to flow passages 70.

Preferably, wafers 64 are sufficiently thin as to provide thermal equilibrium between the wafers and the coolant flowing in the flow passages. This enables the coolant to approach the maximum limiting temperature of the wafer material before it is introduced onto the blade surface. In this manner, the cooling capability of the fluid is completely exploited and the coolant flow may be minimized, and the system provides transpiration cooling of the blades. By way of example, wafers 64 may be between about 0.002 and 0.050 inch in thickness. Wall 62 is preferably constructed with wafers so that the wall may be cooled in the same manner as the blades.

Flow passages are substantially flared from the restrictor passages 72 which are set back from the edge surface so that the fiow resistance of coolant through restrictor passage 72 is relatively insensitive to heat transfer on the face of the blade.

The wafers forming the blades 60 and the wall 62 may be assembled and bonded together in a manner as hereinbefore described. The assembled wafers may then be mounted to housing 74 by sliding the assembled wafers into slot 76 so that shoulder 78 of the assembled wafers abuts shoulder 80 of the housing.

FIG. 11 illustrates another embodiment of a wafer for blade 60. Wafer 64a comprises a pair of distribution channels 66a and 66b connected to distribution channel 66 for providing coolant to flow passages 70. The provision of flow passages 70 on each edge surface of the Wafer provides coolant flow to both exposed surfaces of the blade formed by wafers 64a.

FIG. 12 illustrates a pair of waters 64b and 640 which, when stacked alternately together, provide coolant flow to the surface of a blade formed by wafers 64c and 6415. Distribution channel 66 provides coolant flow through restrictor passages 72 to flow passages 70 disposed on a single edge surface of the wafer. Wafers 64b and 64:: are alternately assembled so that flow passages 70 are alternately provided on opposite sides of the blade, thereby cooling the blade.

The blade assembly illustrated in FIG. 10 is particularly useful as a rotor blade adapted to rotate in the direction indicated by arrows 82. The rotor shaft (not shown) would be disposed somewhat below FIG. 10 at a position such that wafers 64 of blades 60 would extend radially. Since the wafers 64 are radially disposed from the axis of rotation of the blades, the wafers support the structural loads imposed upon the blades. Thus, the bond between adjacent wafers is not required to support structural loads.

In FIG. 13 there is illustrated a blade construction utilizing a plurality of radially disposed wafers 64 constructed within a porous shell 84. Ribs 86 may be provided between the exterior surface of wafers 64 and the interior surface of porous shell 84 to provide chambers 88 within the porous shell to more effectively utilize the porosity of shell 84. Thus, coolant permitted to flow through flow passages 70 into chamber 88 is dispersed within the chamber 88 to provide more evenly distributed coolant flow through porous shell 84 to cool the blades.

The blades constructed in accordance with the present invention may be used as stator blades as well as rotor blades. The completed blades are mounted to a supporting structure, such as wall 12 in FIG. 1 or wall 62 in FIG. 10. In the case of FIG. 1, chamber 16 is in fluid communication with a suitable coolant manifold (not shown) which in turn is in fluid communication with a source of coolant (not shown). In the case of FIG. 10, distribution channels 66 are in fluid communication with coolant manifold 68. In either case, a suitable pump (not shown) may be utilized to aid in the delivery of coolant to the flow passages in the wafers. In the case of a rotor, such as illustrated in FIG. 10, coolant manifold 68 may be in communication with the coolant supply through suitable conduit means and manifold arrangements (not shown) in the rotor shaft (not shown).

The attachment of the completed blade to the supporting structure may be accomplished by any suitable securing technique such as by bonding or bolting the blade to the structure, or, as shown particularly in the case of FIG. 10 where radially disposed wafers are utilized, by simply constructing wafers which provide an integral relationship with the wall.

The present invention thus provides improved blades and blade assemblies capable of being effectively cooled. In the case of the embodiments illustrated in FIGS. l-9, the pores meter the flow of coolant to the surface of the blade. When slots are used, the slots provide film cooling of the blade by permitting a thin film of coolant to be dispersed over the surface of the blade. Furthermore, as shown particularly in the embodiment of FIG. 7, the slots may be provide with a tortuous path in close proximity with the surface of the blade so that coolant flowing through the slots will cool the blade surface by convection before being discharged onto the surface of the blade to filmcool the blade. Furthermore, portions of the blade may be convection cooled by means of extended channels such as channels 24 and 42 in FIGS. 1, 4, and 8. The blades illustrated in FIGS. 1-9 are particularly useful as stator blades although they may be used as rotor blades if desired.

In the case of the embodiments illustrated in FIGS. -12, the wafers are disposed substantially radially so that structural loading is supported by the wafers with a minimum of loading on the bonds between the wafers. The wafers preferably include flow restrictor passages set back from the edge surface so that coolant flow through the restrictor passages will be independent of local heat transfer conditions at the edge surface. Furthermore, the wafers are preferably thin enough as to permit thermal equilibrium between the wafers and the coolant in the flow passages, thereby providing transpiration cooling of the blades. In addition, as coolant is discharged onto the surface of the blade it forms a thin film over the surface of the blade thereby film-cooling the blade surface.

What is claimed is:

1. A blade for a turbine, compressor or the like, said blade comprising: a stack of a plurality of discrete wafers, each wafer having planar surfaces and edge surfaces, the edge surfaces of the wafers together forming a fluid-diverting surface of the blade, a planar surface of each wafer being bonded to a planar surface of an adjacent wafer and all wafers forming a unitary blade structure; a controlled pattern of fiow passages on a planar surface of each wafer; a controlled pattern of slots formed at an edge surface of each wafer; each slot being in fluid communication with a flow passage on each of said wafers; and dclivery means for delivering coolant to said flow passages; said wafers being sufliciently thin as to permit thermal equilibrium between the wafers and the coolant in the flow passages, whereby the maximum cooling capability of the coolant is exploited.

2. A blade according to claim 1 further including an additional flow passage in a planar surface of each wafer terminating at the trailing edge of said blade.

3. A blade according to claim 2 further including manifold means for delivering coolant to said additional flow passages.

4. A blade according to claim 1 wherein at least some of said slots include a curved portion directed toward the trailing edge of said blade.

5. A blade according to claim 4 wherein the curved portion of the slots is arranged in an oblique angle.

6. A blade according to claim 1 wherein the thickness of each wafer is between about 0.002 inch and 0.030 inch.

7. A blade for a turbine, compressor or the like, said blade comprising: a stack of a plurality of discrete wafers, each wafer having planar surfaces and edge surfaces, the edge surfaces of the wafers together forming a fluid-diverting surface of the blade, a planar surface of each wafer being bonded to a planar surface of an adjacent wafer and all wafers forming a unitary blade structure being substantially radially disposed; a controlled pattern of flow passages on a planar surface of each wafer, said fiow passages terminating at an edge surface thereof; and delivery means for delivering coolant to said flow passages; said wafers being sufiiciently thin as to permit thermal equilibrium between the wafers and the coolant in the flow passages, whereby the maximum cooling capability of the coolant is exploited.

8. A blade according to claim 7 wherein each flow passage includes a restrictor passage for metering coolant flow to each edge surface.

9. A blade according to claim 8 wherein said restrictor passages are set back from said edge surface, whereby coolant flow resistance through said restrictor passages will be independent of local heat transfer conditions at the edge surface.

10. A blade according to claim 7 wherein the thickness of each wafer is substantially between about 0.002 inch and 0.050 inch.

11. A blade according to claim 7 wherein said blade is a rotor blade adapted to be rotated about an axis and the bonds between adjacent planar surfaces support a minimum of structural loading as the rotor is rotated.

12. A turbine engine comprising a stator and a rotor, said rotor being adapted to rotate about an axis; stator blades mounted to stator; rotor blades mounted to said rotor, said rotor blades comprising: a stack of a plurality of discrete first wafers, each first wafer having planar surfaces and edge surfaces, the edge surfaces of the first wafers together forming a fluid-diverting surface of the rotor blade, a planar surface of each first wafer being bonded to a planar surface of an adjacent first wafer and all first wafers forming a unitary blade structure being substantially radially disposed so that the bonds between the first wafers support a minimum of structural loading as the rotor is rotated; a controlled pattern of flow pas sages on a planar surface of each first wafer, said flow passages terminating at an edge surface thereof; and delivery means for delivering coolant to said flow passages; said first wafers being sufliciently thin as to permit thermal equilibrium between the first wafers and the coolant in the flow passages, whereby the maximum cooling capability of the coolant is exploited.

13. A device according to claim 12 wherein each flow passage includes a restrictor passage for metering coolant flow to each edge surface.

14. A device according to claim 12 wherein said restrictor passages are set back from said edge surface, whereby coolant flow resistance through said restrictor passages will be independent of local heat transfer conditions at the edge surface.

15. A device according to claim 12 wherein said stator blades comprise a stack of a plurality of discrete second wafers, each second wafer having planar surfaces and edge surfaces, the edge surfaces of the second wafer together forming a fluid-diverting surface of the stator blade, a planar surface of each second wafer being bonded to a planar surface of an adjacent second wafer and all second Wafers forming a unitary blade structure; a controlled pattern of flow passages on a planar surface of each second wafer; a controlled pattern of slots formed at an edge surface of each second wafer; each slot being in fluid communication with a flow passage on each of said second wafers; and delivery means for delivering coolant to said flow passages; said second wafers being sufficiently thin as to permit thermal equilibrium between the second wafers and the coolant in the flow passages, whereby the maximum cooling capability of the coolant is exploited.

16. A device according to claim 15 further including an additional flow passage in a planar surface of each second wafer terminating at the trailing edge of said blade.

17. A device according to claim 15 wherein at least some of said slots include a curved portion directed to- Ward the trailing edge of said blade.

18. A turbine engine comprising a stator and rotor, said rotor being adapted to be rotated about an axis; stator blades mounted to said stator; rotor blades mounted to said rotor, some of said blades comprising a stack of a plurality of discrete wafers, each wafer having planar surfaces and edge surfaces, the edge surfaces of the wafers together forming a fluid-diverting surface of the blade, a planar surface of each wafer being bonded to a planar surface of an adjacent wafer and all wafers forming a unitary blade structure; a controlled pattern of flow passages on a planar surface of each wafer; a controlled pattern of slots formed at an edge surface of each wafer; each slot being in fluid communication with a flow passage on each of said wafers; and delivery means for delivering coolant to said flkow passages; said wafers being sufiiciently thin as to permit thermal equilibrium between the wafers and the coolant in the flow passages, whereby the maximum cooling capability of the coolant is exploited.

19. A device according to claim 18 further including 9 10 an additional flow passage in a planar surface of each 2,828,106 3/1958 Schramm et a1.

wafer terminating at the trailing edge of said blade. 2,853,271 9/1958 Findley.

20. A device according to claim 15 wherein at least 3,301,526 1/1967 Chamberlain. some of said slots include a curved portion directed to- FOREIGN PATENTS ward the trailing edge of said blade.

5 1,064,757 9/1959 Germany. References Cited UNITED PATENTS JR., Primary Examiner 2,701,120 2/ 1955 Stalker. CL 2,786,646 3/1957 Grantham. 10 41 22 2,825,530 3/1958 Schum et a1. 

